I'm assuming Windows XP, but Windows 2000 is similar, previous versions are a bit different.
Right click on My Network Places, click Properties. Select Make New Connection. Click Next. Select "Connect to the network at my workplace". Click Next. Select Dialup Connection, click Next. Enter a name, phone number, etc as prompted. Enter a description for the connection.
I will revert to Mr Marshall for the ISDN dialup portion of your question - not sure if you're in the UK or not and using BT Race or something like that. I'm assuming you are not in the US, as all we need to do is plug in an analog modem line to the BCM and run out the door...